Automatic safety switch for vehicles



Sept. 20, 1938. E. D. LAWSON 2,130,500

AUTOMATIC SAFETY SWITCH FOR VEHICLES Filed Aug. 10, 1935 V Patented Sept'ZO, 1938- AUTOMATIC SAFETY SWITCH FOB VEHICLES Edward D. Lawson, Park Ridge, Ill.

Application August 10,

6 Claims.

'This invention relates to safety switches, but is particularly concerned with switches, adapted for use in the electrical circuit of an automotive vehicle, of such construction that the circuit shall automatically break if the vehicle on which the switch is used should turn over in any way beyond some predetermined angle, the purpose of the switch being to cause the circuit to become dead, thus stopping the engine and eliminating the danger of fire from electrical origin.

A switch of this kind intended for use on auto motive vehicles and particularly motor cars, is subjected to tremendous jars and shocks. Where the switch contains a fluid, it is quite a problem to prevent undesired movement or surging of the fluid without introducing features of construction which complicate the switch and increase its cost.

One 01 the objects of the present invention is to provide a fluid type safety switch such for example as a mercury type switch which shall be simple and inexpensive in construction and in which means shall be provided to prevent undesired surging of the fluid during the normal operation of the motor vehicle even though it be operating over extremely rough roads or other ground. I It is another object of the invention to provide a switch of this type having means which shall cooperate withcertain natural forces tending to maintain the body of the fluid in a certain pre- 7 determined position and shape until the abnormal forces developed by the vehicle turning over or tilting beyond a predetermined angle shall be sumcient to breakdown or alter this status.

The invention consists in certain features of construction and in the combination and arrangement of the several parts which will be hereinafter fully described. The preferred embodiment is illustrated in the accompanying drawing.

In the drawing: Fig. l is a perspective view of the switch with the face plate removed in order to expose the interior construction. Fig. 2 is a longitudinal sectional view of one of the switch tubes removed from the casing and from its cushioning holder.

Fig. 3 is a cross-sectional view through one of the tubes just above the top level of the mercury and illustrating a suppressor plate carried by one of the electrodes, and

Fig. 4 is a perspective view of a pair of cushion blocks for holding the tube element in position in the switch housing.

The switch casing or housing as a whole is designated by the reference 5. It may be com.-

1935, Serial No. 35,648

posed of a' number of materials, but is preferably made of a molded substance which is a good electrical insulator. As here shown, it is of substantially rectangular shape and is of suilicient depth to provide a recess for the accommodation'of two switch tubes, later to be described, in superposed relation.

Formed in the body of the casing 5 is a crosslike depression comprising the aligned portions 6-45 and 1i'. Centrally, the depression is enlarged and shaped to receive and hold snugly two superposed blocks 8 and 8' of cushion material to be described in detail later.

In the cross-like depression before described, there are two mercury switch tube elements 9 and I0 of similar construction. The tube element 9 is arranged at the bottom of the recess and extends diagonally across the casing. The tube element i0 is spaced above the tube element 9 and likewise is positioned diagonally but substantially at right angles to the first mentioned tube. V

In Fig. 4 there is illustrated the two cushion blocks 8 and 8' in superposed condition and in the relation which they occupy when in the easing 5. These blocks are preferably composed of rubber of a fairly firm texture and yet having sufiicient resilience to permit being pressed into position in the opening provided therefor'in the casing 5, a slight compression of the block holding it firmly in position.

Each block is provided with a cylindrical centrally arranged hole I of a size substantially the same as the external diameter of the switch tube element intended to be positioned therein. By making a snug flt it is possible to press the tube element into the opening H and have the block firmly holding the same. It will be understood that block 8 receives-tube designated in in Fig. l and that block 8' receives the tube marked 9 in the same view.

As is clearly illustrated in Fig. 1, the depressions 6-6, in the housing I are slightly greater in size than the tube, thus providing a clearance space around the tubes in order to prevent any possible contact of the tube with the adjacent wall of the housing 5. In other words,the two tube elements, by means of the blocks 8-8 are firmly held. and positioned against movement in any direction and with the clear space separat ing the tubes from the various parts of the housing and from each other. In Fig. 2 I have illustrated one of the switch tubes independently of the cushion holding block and removed from the switch housing 5. Inasmuch as the two tubes are of like construction, a

description of one will suffice for both. It is composed of a glass tube ii of substantially cylindrical shape, closed at one end I 3 bythe substantially dome-shaped portion. At the lower end, the glass walls are pressed together, providing the solid portion ll through which the electrodes l5 and I6 pass from the exterior to the interior of the tube. Inthe lower end of the tube I have provided a body of mercury I1. I prefer mercury for reasons which will later appear.

The upper part i8 of the tube is preferably filled with an inert gas. It is known that the molecules at the surface of a liquid are subjected to a force tending to draw them inward. This force, in eiiect, is like pressing the surface toward the inside as though by a tough elastic sheet stretched over the surface. The final result is to shape the liquid so that it shall tend to have the least possible surface, 1. e. that of a sphere. This result does not entirely obtain in all instances, but there is usually considerable curvature to the top sur face of the liquid. This contracting force is usually termed surface tension. In the case of mercury, the molecular force is relatively great so that the surface tension is likewise considerable and hence results in a very pronounced curvature at the top surface. This, I have indicated in Fig. 2 at H. The pull seems to be the greatest adjacent the wall of the tube so that the liquid surface assumes a curve of smaller radius at that place as indicated at l9.

As an aid in checking the tendency of the mercury to surge when the vehicle is subjected to heavy jolting or jarring, I provide a plate or disc 20 at the end of one of the electrodes of the tube.

The disc or plate 20 as shown, is positioned so that it contacts the upper surface of the mercury when the tube is in normal operating position. It thus may be said to act as a surge suppressor because it assists the molecular forces in holding the mercury in position.

I I also prefer to provide a supplementary electrode portion 20 of arcuate form. As shown it is aflilxed to the electrode that carries the plate 20. The portion 20 aids in preventing surging because the mercury is confined at the top by the plate 20 and more or less anchored by the arcuate electrode portion 20. This construction also provides intermediate of the electrodes, por-, tions relatively close together and which are bridged by the mercury even though a considerable portion may have flowed away from the bottom of the tube. It will thus be obvious that there are several restraining influences which prevent undesired surging of the mercury. There is force of gravity which is considerable due to the density of mercury. Furthermore, since the air has been exhausted and replaced with an inert gas, there is no air that'c'an be trapped under the mercury. If air were present and became trapped under the mercury, it would act like a. spring to agitate the mercury, which would be objectionable.

Another restraining influence is the molecular force which produces a surface tension that draws the top surface of the mercury inwardly so that said top surface tends to take on a dome shape.

However, because of the fixed position of the plate 20 with respect to said top surface, said surface tension is resisted and the surface is flattencd out so that an upward thrust is produced against the underside of the plate. This prevents any incipient tendency of the mercury to surge through inertia set up by the jolting of the vehicle, from becoming effective. of course, when the vehicle containing the switch actually turns over or reaches some predetermined angle then the forces mentioned are overcome and the mercury flows to the other end of the tube, thus breaking the electrical circuit, thereby causing the engine to stop and making all parts electrically dead.

I prefer also, so to form, position and arrange the plate 20 that it will act as a positive mechanical valve. To this end, .the plate is eccen trically disposed within the tube as best shown' in Fig. 3 so that there is avery small space 2| between the wall of the tube and the edge of the plate at one side and a substantially larger space 22 diametrically opposite. The space 22, therefore, becomes the gate through which the mercury flows when'the vehicle is tilted or turns over.

It is believed, from the foregoing, that the operation of the switch will be understood. How ever, referring briefly to Fig. 1, it will be seen that one electrode of one tube is electrically connected to one electrode of the other tube by a conductor 23. The other electrode of tube 9 is connected to the binding post 24 by the conductor 25 and the other electrode of tube I0 is connected to the binding post 26 by conductor 21. The conductors 29 and 30 respectively connected to the binding posts 2 and 26, it will be understood, form a part of the electrical system of the vehicle to which the switch is aflixed.

It will be observed that each. mercury tube ele-.

ment is a very simple construction so that it lends itself to rapid and practically automatic manufacture and hence can be produced at low cost. The two mercury tubes, in turn, are very quickly and easily assembled in the casing 5 and there held in place by cushion blocks 8-8 in which the tubes have been placed prior to positioning in the casing 5.

In practice a face plate, not shown, is fastened to the casing 5 so as to prevent tampering with the switch. The face plate also aids in holding the blocks 8 against undesired movement laterally of the casing.

It will also be understood that the switch is intended to occupy a vertical position, i. 'e. the tubes are positioned in vertical planes. Conveniently the rear face 5' of the casing can be placed against a vertical wall of the motor vehiclebody and the casing held in place by suitable fastening devices.

It will further be obvious that-the switch may be fully assembled at the factory and that no special operations are necessary to condition the switch for use, except to see that the switch is mounted in a vertical plane.

While in describing the invention, I have referred in detail to the arrangement and construction of the various parts, it will be understood that changes may be made provided such changes come within the scope of the appended claims.

I claim as my invention:

1. A switch of the kind described embodying therein a pair of tubes oppositely inclined from the perpendicular, the tubes being arranged in different vertical planes, means providing a cushion having openings therein through which said tubes extend with a snugiit so as to be supported by said means, a quantity of mercury normally disposed in the bottom end of each tube, and a pair of electrodes associated with each tube and opening thereinto to engage in the mercury in the respective tubes, the electrodes of both tubes being adaptedfor connection in the circuit to be controlled.

2. A switch of the kind described embodying therein a pair of tubes oppositely inclined from the perpendicular, the'tubes being arranged in diflerent vertical planes and crossing each other to present a substantially X form, cushion means supporting said tubes at the point where they cross each other, a quantity of mercury normally disposed in the bottom end of each tube. and a pair of electrodes associated with each tube and opening thereinto to engage in the mercury in the respective tubes, the electrodes for both tubes being adapted for connection in the circuit to be controlled.

3. A switch oi the kind described embodying therein a casing having an X shaped depression therein formed by a pair of channels which intersect one another. said depression having an enlargement at said intersection, a pair of tubes oppositely inclined from the perpendicular, the tubes being arranged in diflerent vertical planes but crossing each other at said enlargement. a quantity of mercury normally disposed in the bottom end of each tube, a pair of electrodes associated with each tube and opening thereinto to engage in the mercury in the respective tubes. the electrodes for both tubes being adapted for connection in the circuit to be controlled, and a cushion block disposed in said enlargement and surrounding the central portion of each tube and serving to hold the tube in place in said casing.

4. A switch element embodying a tube, a quantity of liquid, adapted to conduct electricity, normally disposed in the bottom end of the tube, a pair of electrodes associated with the tube and opening thereinto to engage in the said liquid, a plate fixed in said tube against movement and substantially paralleling the top 01' the liquid when the tube is in normal position, and a supplementary electrode portion carried by one of the electrodes and spaced below the said plate.

5. A switch element embodying a tube, a quantity of liquid, adapted to conduct electricity normally disposed in the bottom end of the tube, a pair of electrodes associated with the tube and opening thereinto to engage in the said liquid, a plate, iixed in said tube against movement and substantially paralleling the top 01 the liquid when the tube is in normal position, and an arcuate electrode portion carried by one of the electrodes below said plate.

6. A switch element embodying a tube, a quantity oi liquid adapted to conduct electricity-normally disposed in the bottom end oi the tube, a pair or electrodes associated with the tube and opening thereinto to engage in said liquid, a plate carried by one of the electrodes and substantially paralleling the top of the liquid when the tube is in operable position, said plate being eccentrically disposed within the tube. V

EDWARD D. LAWSON. 

